I'm looking into basically building my own Sync Strike, because $40 is way more than what I'm willing to pay for essentially nothing more than an LM1881 breakout board, but I'm stuck a bit trying to understand the sync signal logic. The LM1881 doesn't output HSYNC, but you can derive HSYNC from VSYNC and CSYNC, and this is where it gets confusing. There are posts online indicating that HSYNC is (C NAND V) AND C, but this seems like the exact opposite of what it should be, as sync pulses are active-low, right? So, for the following waveforms:
the truth table would be
C V H
0 0 1
0 1 0
1 0 1
1 1 1
which is (C NOR V) OR C. The NAND solution seems to be based on the assumption that the sync pulses are active-high, which doesn't seem to be the case. Can anybody more familiar than me with this stuff clarify which is correct?
Edit: fixed the truth table
Code:
C--___---_-_-_--
V--___----------
H--------_-_-_--
V--___----------
H--------_-_-_--
the truth table would be
C V H
0 0 1
0 1 0
1 0 1
1 1 1
which is (C NOR V) OR C. The NAND solution seems to be based on the assumption that the sync pulses are active-high, which doesn't seem to be the case. Can anybody more familiar than me with this stuff clarify which is correct?
Edit: fixed the truth table